The present invention relates to hybrid power systems for driving motor vehicles utilizing an electric motor and flywheel combination, and is more particularly directed to a hybrid power system for driving a motor vehicle with the system being capable of applying braking energy to recharge the electric batteries that power the electric motor and to recharge the kinetic energy in the flywheel.
The interest in hybrid power systems of this type has arisen primarily because of the increasing cost of fuel and the inefficiency of operation of conventional internal combustion engine power systems for motor vehicles. When an internal combustion engine is the sole source of power for a motor vehicle, the engine must be of sufficient size and capacity to deliver maximum power loads on demand for acceleration, even though such demands are occasional and the normal operation is at a much lower power demand range. The engine could operate much more efficiently if it could operate substantially continuously within an optimum efficiency operating range without maintaining the capability of providing an output substantially greater than this range. Utilizing an engine requiring operation only in the optimum efficiency operating range would allow the use of a less powerful and a much lighter engine with the obvious attendant economy.
Electric motors have been developed as substitutes for internal combustion engines, but they have been found to be generally unacceptable for universal usage in motor vehicles because of the limited energy storage capacity of electric storage batteries in relation to weight limitations for efficient vehicle application and because of the extended time that batteries must be out of operation for recharging.
Flywheels have also been utilized in attempts to store kinetic energy that can be delivered during times of peak load demand so that an internal combustion engine or an electric motor need not have the size and capacity necessary for delivering sufficient power in themselves during periods of acceleration. Flywheels also have the advantage of receiving energy generated during braking of the vehicle so that such energy that is normally dissipated as heat and not reused can be regenerated in the flywheel for subsequent delivery during peak load demands during acceleration. However, flywheels have the disadvantage of a reduction in the output speed of rotation as the energy is being dissipated, which is usually during periods of vehicle acceleration when rotational speeds are increasing otherwise.
Hybrid power systems have been designed utilizing flywheels in combination with internal combustion engines or with electric motors or with both, and internal combustion engines have been utilized to provide energy for charging batteries that provide power for electric motors, but none of these systems has found commercial acceptance.
Nyman U.S. Pat. No. 3,665,788 discloses a type of power system in which a flywheel is combined with an internal combustion engine to deliver energy during peak demands and to be recharged by the regenerative energy developed during braking. In this patent the flywheel is connected through a variable transmission and planetary gears to control the delivery of energy from and to the flywheel.
Dooley U.S. Pat. No. 3,493,066 discloses an internal combustion engine that has an auxiliary power take-off for charging a battery that drives an electric motor that in turn charges a flywheel, with the flywheel being utilized periodically to apply additional power through the internal combustion engine to handle peak load conditions. Nyman U.S. Pat. No. 4,187,741 discloses another example of combining a flywheel with the primary engine of a motor vehicle to apply peak power that can be regenerated during braking.
Helling U.S. Pat. No. 3,923,115 discloses the combination of an internal combustion engine, electric motor and flywheel wherein the electric motor and internal combustion engine are combined through a differential to apply power to the drive shaft while the flywheel is connected to the output of the internal combustion engine to apply energy during peak load, but as the energy from the flywheel is being dissipated, the rotational speed of the output will be decreasing even though the vehicle is accelerating. During braking, the regenerated energy is transferred back to the flywheel and through the electric motor, as a generator, to the battery. Also, the internal combustion engine is utilized to charge the flywheel and battery when its full power is not being utilized to drive the vehicle, but the batteries can not be charged during the periods of time that the electric motor is being utilized to deliver motive power.